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Tubelab Discussion and support of Tubelab products, prototypes and experiments

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Old 8th February 2019, 06:22 AM   #61
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Hi George,

Can you please take a pic of the old and new board side by side.. Trying to figure out if it'll fit in my current wood open top cabinet. Thanks a lot.
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Old 8th February 2019, 03:12 PM   #62
boywonder is offline boywonder  United States
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Very Cool........
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Old 8th February 2019, 03:25 PM   #63
Tubelab_com is offline Tubelab_com  United States
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Using nothing more than a voltmeter to test the voltages, set the bias on the output tubes, and plate voltage on the drivers, the board came right up and plays nice. It currently has Chinese 2A3's in it which have been worse case in the filament regulator department.

Quote:
would it be possible to add test points to the board?
There will be at least one more iteration of the layout to fix some minor parts fitment issues. I'll look into adding some probe points for the major voltages, but I'm hesitant to mess with success too much.

Quote:
another aspect that can be (maybe) improved - please refer to the the MOSFETs and heat-sinks
The number one request for the new board was to improve this area. People complained about the dual heat sink, often saying it's hard to find (Digikey still has them), the area is too crowded, and gets too hot.

I addressed these concerns by incorporating individual heat sinks that are quite common (yes 1 inch tall), spaced then further apart, and modified the circuit to reduce the dissipation. After playing for over an hour I can put my finger on the heat sink without burns. NOTE, DON'T do this, they still carry B+ voltage unless insulators are used. The board can be assembled with the heat sinks (and other parts, except tube sockets) on the bottom side to allow for close to the top plate mounting. My next build up will be done this way to verify placement before sending out for boards.

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take a pic of the old and new board side by side.....if it'll fit in my current wood open top cabinet.
In order to accommodate the heat sink requests, and the requests to increase the spacing between the output tubes, the board got larger in both X and Y directions. The placement of all 5 tubes moved with respect to each other, so I doubt existing cabinetry will work.

I'm going to let it play for the rest of the day while I work on Tubelab's taxes. Maybe later I'll try some different tubes or take some measurements.
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Old 8th February 2019, 04:13 PM   #64
Evenharmonics is offline Evenharmonics  United States
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Quote:
Originally Posted by zman01 View Post
In my experience, this place was a tight fit for the sinks and the height was a challenge
It's a high heat area too. I once had a pair of caps which the cover wrap melted due to the heat from those heat sinks.
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Old 8th February 2019, 06:08 PM   #65
Tubelab_com is offline Tubelab_com  United States
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Quote:
It's a high heat area too.
Well understood, and fixed.

The TSE was designed with 45's in mind. It was the early 2000's and good used tubes could still be found on Ebay, in flea markets, and at hamfests for $5 to $10 each! At that time many of my amps were hand wired, and constantly evolving. Most were actually Push Pull amps using 6L6GC's or KT88's.

The discovery of "PowerDrive" brought the mosfets and PC boards into the picture. I can find pictures and Eagle files of at least 4 different versions of what became the TSE. Often the board changed to fit whatever parts I could get surplus, and all boards were DIY like the one in these pictures. They all went to my technical friends, who often built them themselves.

I couldn't make enough of them so myself and some friends decided to pool our money and get a batch of boards made for our 45 amps. I did the "final layout" for that design based on parts in the 2003 or 2004 Digikey catalog. We even got a bunch of different caps and took them into the plant to analyze them and picked the best....this is the reason for the huge cathode bypass caps. As with this board I made a prototype board to test the layout before spending money on a batch of boards. That proto board from 2004 is the one in the foreground of the 3 boards picture in post #63. It still works too!

There have been ZERO changes in the TSE board since then, but people (including myself) stuck bigger and bigger tubes into it, and line voltages keep going up, so it runs a lot hotter than in 2004. Time for a change.

In spite of the heat, the TSE has been a popular amp design once people got over the "sand in the signal path" thing. Therefore, I'm hesitant to make any major changes. The most popular request was "make it bigger." The amp looked funny when some fat 300B's were installed and they nearly touched each other. I stretched the board to the biggest size that would fit the mailing materials I use and used most of the room around the heat sinks, tube spacing, and the new heater supply (more caps).

The TSE was always marginal with 2A3 tubes since that eat 2.5 amps each. That was another design criteria for the new heater circuit. It has been playing for 3 hours now with 2A3's running 75 mA each at 125 volts AC line and nothing is excessively hot. I plan on tweaking some resistor values to even out the heat once 45's and 300B's are tested.

After about an hour I smelled something hot. Investigation revealed that the B+ choke I borrowed from an old HP audio oscillator really doesn't like 170 mA of current through it.
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Old 9th February 2019, 02:55 AM   #66
colnago55 is offline colnago55  United States
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Here's another suggestion:

Would it be possible label the parts on both sides of the board to facilitate dual side assembly?
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Old 10th February 2019, 03:28 PM   #67
boywonder is offline boywonder  United States
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.....So no viable alternatives to the 5842?
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Old 10th February 2019, 11:28 PM   #68
Captn Dave is offline Captn Dave  United States
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One more suggestion if it's not too late for consideration.

A fifth mounting hole in the center of the board somewhere might be a good idea. The shorter board flexes a bit when tubes are inserted and that will become more evident with the longer board.

A pair on the centerline at the edge would rock but I don't see a suitable location.
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Old 11th February 2019, 12:47 AM   #69
tomchr is offline tomchr  Canada
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Thought I'd comment as an FYI in case you'd ever want to improve on the toner transfer process.

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Originally Posted by Tubelab_com View Post
This is a DIY proto board that was made using an iron on toner transfer method. My printer can't make two identical prints, and the paper itself goes through thermal shock when the hot iron hits it. These protos will have registration issues between the two sides and well as several other less than desirable traits like lack of plated through holes.
I've had good luck with HP brochure paper for toner transfer. It's a glossy and slightly heavier paper than regular copier paper. It's intended for laser printer use.
For the transfer, I use a cheapie laminator that I picked up new on eBay for something like $25. I had to chop off a part of the cover so the board would go through without interference. The heat and pressure of the laminator works really well for toner transfer. I run the board through a few times to get it nice and hot. Then sandwich between top/bottom layer printouts and run it through the laminator another few times. I'm able to get 0.25 mm registration on a good day.

Quote:
Originally Posted by Tubelab_com View Post
They will never leave my lab, so I live with the drawbacks in order to eliminate the time and $$$$ for one or two off boards.
Makes perfect sense to me. Also, if it ain't broken, don't fix it. With large parts you can live with quite a bit of registration error - especially for a prototype.

Tom
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Old 11th February 2019, 09:22 PM   #70
tgreese is offline tgreese  United States
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Quote:
Originally Posted by boywonder View Post
.....So no viable alternatives to the 5842?
How about 6C45pi?


E180F is also suggested in earlier posts.

Last edited by tgreese; 11th February 2019 at 09:27 PM.
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